1. Technical Field
The present invention relates to thin film transistors and, particularly, to a carbon nanotube based thin film transistor.
2. Discussion of Related Art
A typical thin film transistor (TFT) is made of a substrate, a gate electrode, an insulation layer, a drain electrode, a source electrode, and a semiconductor layer. The thin film transistor performs as a switch by modulating an amount of carriers accumulated at an interface between the insulation layer and the semiconducting layer.
Generally, the material of the semiconductor layer is amorphous silicone (a-Si), poly-silicone (p-Si), or organic semiconducting material. The carrier mobility of an a-Si TFT is lower than a p-Si TFT. However, the method for making the p-Si TFT is complicated and has a high cost. The organic TFT has the virtue of being flexible but has low carrier mobility.
Carbon nanotubes (CNTs) are a novel carbonaceous material and have received a great deal of interest since the early 1990s. Carbon nanotubes have interesting and potentially useful heat conducting, electrical conducting, and mechanical properties. Further, there are two kinds of carbon nanotubes: metallic carbon nanotubes and semiconducting carbon nanotubes determined by the arrangement of the carbon atoms therein. The carrier mobility of semiconducting carbon nanotubes along a length direction can reach about 1000 to 1500 cm2V−1 s−1. Thus, a TFT employing a semiconductor layer adopting carbon nanotubes has been produced.
However, the carbon nanotubes in the conventional TFT are distributed as a disordered carbon nanotube layer or perpendicular to the substrate as a carbon nanotube array. In the disordered carbon nanotube layer, due to disordered arrangement of the carbon nanotubes, the paths for carriers to travel are relatively long resulting in low carrier mobility. Further, the disordered carbon nanotube layer is formed by printing a mixture of a solvent with the carbon nanotubes dispersed therein on the substrate. The carbon nanotubes in the disordered carbon nanotube layer are joined or combined to each other by an adhesive agent. Thus, the disordered carbon nanotube layer has a hardened structure and is not suitable for being used in a flexible TFT.
In the carbon nanotube array, the carbon nanotubes are perpendicular to the substrate. However, although the carbon nanotubes have good carrier mobility along the length direction, the carrier mobility of the carbon nanotube array along a direction parallel to the substrate is relatively low.
In sum, the two kinds of carbon nanotube structure employed in the conventional TFT have low carrier mobility and poor flexibility.
What is needed, therefore, is a TFT in which the above problems are eliminated or at least alleviated.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present thin film transistor, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.